Question

In Rails it is possible to declare a transitive relation as follows:

class Author < ActiveRecord::Base
    has_many :authorships
    has_many :books, :through => :authorships
end

Is it possible to do something similar in Hibernate? When I call author.getBooks() I want Hibernate to know to join authors with authorships with books.

Answer 1

I don’t believe there is anything in Hibernate’s mappings that can accomplish this, but you could simply add a getBooks() method to your Author class that calls the correct method on the authorships property:

public class Author {
    public Collection<Book> getBooks() {
        if (this.authorships != null) {
            return this.authorships.getBooks();
        }
        return null;    
    }
}

I’m not sure why the ORM would need to know about a transitive relationship between A and C between B, if you can just set that up in the class on it’s own.